单选题 According to the passage, it is TRUE that ______.

A、 in the late 19th century in the United States the dividing line between adolescence and adulthood no longer existed
B、 no one can marry without the permission of his parents until the age of twenty-one
C、 one is considered to have reached adulthood when he has a driver's license
D、 one is not free form the restrictions of child labor laws until he can join the army

【正确答案】 A

【答案解析】[解析] 文章第一段最后一句中的frontier原意为“边境，边缘”，在本句中则指“青春期与成年期之间的分界线”，故应选A。